Abstract: A base portion for use in a bottom nozzle of a fuel assembly in a nuclear reactor includes a top surface, a bottom surface, and a plurality of vertical wall portions arranged in a generally squared grid-like pattern which extend between the bottom surface and the top surface and which define a plurality of non-circular passages passing between the bottom surface and the top surface through the base portion.

Abstract: A fuel assembly for a nuclear water reactor having an upstream end, a downstream end, and a flow interspace between the upstream and downstream ends. Fuel rods are provided in the flow interspace between the upstream and downstream ends. The flow interspace permits a flow of coolant through the fuel assembly along a flow direction from the upstream end to the downstream end. A filter device is provided to catch debris particles in the flow of coolant. The filter device has a first filter zone for a major part of the flow of coolant, and a second filter zone for a minor part of the flow of coolant. The first filter zone has a first filtering efficiency and the second filter zone has a second filtering efficiency. The second filtering efficiency is higher than the first filtering efficiency.

Abstract: A flow distribution device (3) for a reactor, a lower internals (100) of a reactor and a reactor are provided. The lower internals (100) includes: a lower core support plate (2) defining a coolant hole therethrough; a flow distribution device (3) mounted on the lower core support plate (2) and including a distribution annular plate (8) and a distribution bottom plate (9); a vortex suppression plate (7) disposed below the distribution bottom plate (9); a support column (4) defining an upper end connected with the lower core support plate (2) and a lower end passing through the distribution bottom plate (9) to connect with the vortex suppression plate (7); an energy absorption device (5) defining an upper end connected with the vortex suppression plate (7); and an anti-break bottom plate (6) disposed on the lower end of the energy absorption device (5).

Abstract: The present invention relates to a lower end fitting for reducing flow resistance due to an in-core instrument in a nuclear fuel assembly, that is, a lower end fitting (100) having a plurality of flow holes for a nuclear fuel assembly, in which the flow holes (121) are formed under an assembly groove in which an instrumentation tube (131) for a nuclear fuel assembly is inserted, and at least two or more flow holes (121) are formed at a predetermined distance from the central axis (C) of the instrumentation tube (131).

Abstract: A nuclear reactor having an upper internals control rod assembly guide tube formed from upper and lower sections that are connected along a central axial region of the guide tube at an intermediate coupling. An extended control rod axial support is provided for at least some of the control rods over a finite distance within at least one of the interiors of the lower guide tube section or the upper guide tube section.

Abstract: A nuclear fuel assembly having a bottom nozzle with protrusions that extend from the upstream (lower or fluid entry) and downstream (upper or fluid exit) side of a horizontally supported perforated flow plate. The protrusions have a funnel-like shape that gradually decreases the lateral flow area on the upstream side of the perforated flow plate and gradually increases the lateral flow area on the downstream side of the perforated plate. The protrusions on the downstream side are preferably recessed to accommodate the ends of the fuel rods.

Abstract: A pressure-tube nuclear reactor can include an outer shell having an interior to contain a moderator at a first pressure and a coolant plenum to receive the coolant fluid at a second pressure, the second pressure being greater than the first pressure. The reactor also includes a plurality of pressure tubes. Each pressure tube is received within and extends through a corresponding shell tube and is configured to releasably retain at least one fuel bundle. A first end of each pressure tube being coupled to the plenum tubesheet in fluid communication with the plenum chamber and a second end of each pressure tube fluidly connected to a coolant conduit to enable the coolant fluid to flow between the coolant plenum and each pressure tube and to flow from the nuclear reactor for further processing.

Abstract: In a nuclear reactor, a core barrel (46) is disposed in a reactor vessel (41) having an inlet nozzle (44) and an outlet nozzle (45), a core (53) is disposed in the core barrel (46), a lower plenum (58) is partitioned by the reactor vessel (41) and a bottom portion of the core barrel (46), and a downcomer portion (59) is partitioned by the reactor vessel (41) and a side wall of the core barrel (46). The lower plenum (58) includes a straightening member (61) formed of an upper ring (65) and a lower ring (69) in a ring shape, and a plurality of spokes (64 and 68) radially arranged inside the rings (65 and 69), respectively. Heat exchange efficiency is enhanced by uniformly supplying coolant introduced into a pressure vessel to the core from the lower plenum in a radial direction and a circumferential direction.

Abstract: The geometric dimensions and shape of a device for removing solid particles from the cooling medium that is circulated in the primary circuit of a nuclear reactor, in particular a boiling water nuclear reactor, are such that the device can be inserted in lieu of a fuel element or fuel assembly into an empty fuel element or assembly position of the reactor core of the nuclear reactor.

Abstract: The present invention relates to a longitudinally divided emergency core cooling (ECC) duct in order to efficiently inject safety water to core of a pressurized light-water nuclear reactor. The ECC duct includes side supports for preventing the flow-induced vibration in the annular downcomer, and has structural stability while thermally expanding and contracting. A longitudinally divided ECC duct for emergency core cooling water injection of a nuclear reactor is provided on the periphery of a core barrel of a nuclear reactor, includes an emergency core cooling water inlet facing a direct vessel injection nozzle, and extends in a longitudinal direction of the core barrel. The longitudinally divided ECC duct is divided into a plurality of longitudinally-divided ducts in the longitudinal direction of the longitudinally divided ECC duct.

Abstract: A fixed cluster for the core of pressurized-water nuclear reactor including rods and a holder for rods. The holder includes: an upper head; fins extending radially towards the outside from the upper head; systems for mounting the rods and distributed on the fins; and at least two abutment elements on the upper plate of the core, each of the abutment elements protruding longitudinally from a respective fin beyond the mounting systems so as to be vertically oriented towards the top when the fixed cluster is provided on a nuclear fuel assembly.

Abstract: Apparatuses for reducing or eliminating Type 1 LOCAs in a nuclear reactor vessel. A nuclear reactor including a nuclear reactor core comprising a fissile material, a pressure vessel containing the nuclear reactor core immersed in primary coolant disposed in the pressure vessel, and an isolation valve assembly including, an isolation valve vessel having a single open end with a flange, a spool piece having a first flange secured to a wall of the pressure vessel and a second flange secured to the flange of the isolation valve vessel, a fluid flow line passing through the spool piece to conduct fluid flow into or out of the first flange wherein a portion of the fluid flow line is disposed in the isolation valve vessel, and at least one valve disposed in the isolation valve vessel and operatively connected with the fluid flow line.

Abstract: The present invention provides a bottom nozzle filtering device and a debris-preventive bottom nozzle that can be used for a light water reactor (LWR) nuclear fuel assembly. The bottom nozzle filtering device includes a plurality of successively spliced unit plates; a through flow channel is formed between the spliced adjacent unit plates; the flow channel includes a plurality of spaced straight-section flow inlets and straight-section flow outlets, and a flow subchannel communicating; the outlet section of each straight-section flow inlet in the middle splits respectively into two flow subchannels, and the inlet section of each straight-section flow outlet in the middle communicates respectively with the two flow subchannels. The flow direction of the coolant is controlled by the straight-section flow inlet, the straight-section flow outlet, the flow subchannel to prevent unnecessary eddies forming, making the pressure loss effectively controlled and improving the filtering effect.

Abstract: A nuclear reactor comprises a nuclear reactor core disposed in a pressure vessel. An isolation valve protects a penetration through the pressure vessel. The isolation valve comprises: a mounting flange connecting with a mating flange of the pressure vessel; a valve seat formed into the mounting flange; and a valve member movable between an open position and a closed position sealing against the valve seat. The valve member is disposed inside the mounting flange or inside the mating flange of the pressure vessel. A biasing member operatively connects to the valve member to bias the valve member towards the open position. The bias keeps the valve member in the open position except when a differential fluid pressure across the isolation valve and directed outward from the pressure vessel exceeds a threshold pressure.

Abstract: Disclosed is a method for removing a thermal sleeve from a cold leg of a reactor coolant system, which enables removal of an unintentionally separated thermal sleeve without implementation of a pipe cutting operation, preventing invasion of impurities into pipes and securing reliability in repetitious welding of the pipes. In particular, the method enables a remote operation and an underwater operation using wire ropes, thus being capable of minimizing a negative effect on workers due to radiation exposure.

Abstract: A hold-down spring unit for a top nozzle of a nuclear fuel assembly. The hold-down spring unit is coupled to the upper end of the top nozzle of the nuclear fuel assembly. The hold-down spring unit includes a first spring which provides a hold-down force upon the nuclear fuel assembly under start-up conditions or hot full power conditions of a nuclear reactor, and a second spring which provides an additional hold-down force upon the nuclear fuel assembly under start-up conditions of the nuclear reactor. The hold-down margin under start-up conditions or hot full power conditions is reduced, thus enhancing the mechanical and structural stability of the nuclear fuel assembly.

Abstract: Provided is a fuel assembly 1 for a PWR nuclear reactor capable of stably creating transverse flows of coolant for pressing and securing control rods so as to restrain vibration of the control rods in order to restrain the outer surfaces of the control rods and the inner surfaces of control rod guide tubes from being worn, wherein an upper nozzle arranged above the fuel assembly comprises an adapter plate 6 constituting the lower structure of the upper nozzle, a side wall extended along the periphery of the adapter plate, an overhang projected into a space above the adapter plate from the upper part of the side wall, and apertures for attaching control guide tubes and passage holes, which are formed in the passage surface of the adapter plate, and wherein those 15A, 15B, 15C of the passage holes which are located at positions where the coolant impinges upon the overhang are generally arranged, line-symmetric with respect to diagonal lines of the passage surface serving as symmetric axes Q, and ligaments 21, 2

Abstract: A nuclear fission reactor, flow control assembly, methods therefor and a flow control assembly system. The flow control assembly is coupled to a nuclear fission module capable of producing a traveling burn wave at a location relative to the nuclear fission module. The flow control assembly controls flow of a fluid in response to the location relative to the nuclear fission module. The flow control assembly comprises a flow regulator subassembly configured to be operated according to an operating parameter associated with the nuclear fission module. In addition, the flow regulator subassembly is reconfigurable according to a predetermined input to the flow regulator subassembly. Moreover, the flow control assembly comprises a carriage subassembly coupled to the flow regulator subassembly for adjusting the flow regulator subassembly to vary fluid flow into the nuclear fission module.

Abstract: A nuclear fission reactor, flow control assembly, methods therefor and a flow control assembly system. The flow control assembly is coupled to a nuclear fission module capable of producing a traveling burn wave at a location relative to the nuclear fission module. The flow control assembly controls flow of a fluid in response to the location relative to the nuclear fission module. The flow control assembly comprises a flow regulator subassembly configured to be operated according to an operating parameter associated with the nuclear fission module. In addition, the flow regulator subassembly is reconfigurable according to a predetermined input to the flow regulator subassembly. Moreover, the flow control assembly comprises a carriage subassembly coupled to the flow regulator subassembly for adjusting the flow regulator subassembly to vary fluid flow into the nuclear fission module.

Abstract: A debris filter for reactor coolant includes a plurality of adjacent plates defining a plurality of channels therebetween, each of said channels being at an angle to the flow path of the coolant into the filter.

Abstract: Disclosed is an apparatus for removing a thermal sleeve from a cold leg of a reactor coolant system, which removes an unintentionally separated thermal sleeve without pipe cutting, preventing invasion of impurities into pipes and achieving reliable pipe re-welding. The apparatus includes a sleeve removal tool including a corn head formed at a shaft, a pressure plate below the corn head to maximize hydraulic pressure inside a safety injection pipe, a spring connected to the pressure plate to keep the pressure plate unfolded, and a guide wheel to guide the sleeve removal tool into the safety injection pipe, a horizontal movement carrier including bodies connected to each other by a link, a seating rod for seating of the sleeve removal tool, and moving wheels for movement of the horizontal movement carrier, and a vertical movement carrier including first and second anti-separation bars to prevent separation of the horizontal movement carrier.

Abstract: Fuel supports have specially configured flow paths useable in reactor cores to achieve desired levels of flow at given positions. Any number of differently-configured inlet orifices, from three to hundreds, are useable in a given core. Inlet orifice configuration may include diameter sizing or presence of flow blockages such as filters, venturis, choke plates, and/or obstructions. Fuel supports may be positioned within a core plate in the nuclear reactor, with openings for a control blade and instrumentation tubes to pass through or between the fuel supports. Different fuel support configurations may be used at outer core periphery, inner core periphery, and central core portions. Example methods configure fuel support characteristics by examining the effect of modifying flow loss coefficients at particular bundle locations and configuring associated inlet orifices to achieve the modified flow loss coefficients, if the effect is a positive one.

Abstract: In a nuclear reactor core, a lower tie plate assembly is provided with asymmetric features designed to control or vary a loss coefficient as a function of rotation of the associated fuel assembly. An associated method is provided to control the flow of coolant through the associated fuel assembly via rotation of the fuel assembly relative to the fuel support member. Control of the flow can be used to adjust assembly flow rate, assembly power and flow quality within the fuel assembly, among other assembly operational characteristics. Such flow control will impact the flow through other assemblies as well, since core flow remains generally fixed. On a core-wide basis, such flow control can be used to optimize core wide parameters. Optimization parameters of particular interest are the fuel cycle cost and moisture carryover.

Abstract: A telecommunication system is arranged between a trusted automated interactive system and a non-secure agent. The trusted automated interactive portion is operable for bidirectional communications with a caller. The agent portion is arranged to be bridged onto a communication connection between the caller (or network chat user) and the trusted interactive system under certain conditions. Sensitive data transmitted between the system and a calling user may be blocked from being communicated to the agent even while the agent is bridged onto the connection. In one embodiment, information (such as a verification of authenticity of the caller) pertaining to the sensitive data (but not the sensitive data itself) is communicated to the agent.

Abstract: [Problem to be Solved] To suppress problems due to a flow of a primary coolant while easily distributing a flow rate of the primary coolant to fuel assemblies. [Solution] A pressure-loss adjusting member 60 includes: a pressure-loss adjusting hole 62 that can cause light water to pass therethrough in a state with a pressure-loss being increased more than that of when light water flowing around the fuel assembly passes through only a core support plate flow hole formed in a lower core support plate; and a core support plate engaging unit 70 that can be engaged with the lower core support plate by being inserted into the core support plate flow hole.

Abstract: [Problem to be Solved] To easily distribute a flow rate of a primary coolant to fuel assemblies. [Solution] A pressure-loss adjusting member 60 includes: engagement holes 61 into which a plurality of fuel assembly guide pins 24 formed on a lower core support plate 22 can be inserted respectively, the engagement holes being formed in a same positional relationship as a relative positional relationship between positioning holes formed in plural in a lower nozzle; and a pressure-loss adjusting hole 62 that can cause light water flowing around a fuel assembly to pass therethrough in a state with a pressure-loss in the fuel assembly being increased more than that of when the light water passes through only lower core support plate flow holes 23 formed on the lower core support plate 22. Accordingly, the pressure-loss adjusting member 60 can be easily arranged on the lower core support plate 22.

Abstract: A clamp assembly for securing a thermal sleeve and an elbow in a pipe assembly in a nuclear reactor. The clamp assembly comprises a sleeve clamp adapted to be arranged surrounding the elbow at a first joint between the elbow and a thermal sleeve, and comprising a sleeve support adapted to extend across the first joint. The clamp assembly comprises at least one clamp arm with a first end arranged to rest against at least one of a core shroud and a core plate support ring, to provide support for the positioning of the sleeve clamp.

Abstract: A connecting device including a nut, a screw, a body having a bore for screwing the screw to the nut through the bore with the screw abutting an abutment surface of the body, a screw locking device for preventing loosening of the screw. According to one aspect of the invention, the locking device is adapted for axially retaining the screw into the body after unscrewing the screw.

Abstract: Example embodiments are directed to core spray sparger T-box repairs, specifically, to universal core spray sparger T-box weldless clamps having remote-friendly operation and methods of using universal core spray sparger T-box weldless clamps. Example embodiment clamps may be secured without welding to a variety of upper and lower sparger T-box configurations. Example embodiment clamps may be configured to simultaneously engage a sparger T-box in multiple dimensions to allow a universal fit. Further, example embodiment clamps may be accessed, installed, or removed by interacting only with a front side of the example embodiment clamps, thus potentially reducing difficulty and cost in remote access repairs to example clamps.

Abstract: A core spray sparger T-box clamp for a sparger T-box in a shroud of a nuclear reactor pressure vessel, the sparger T-box clamp including: an anchor plate substantially aligned with a closed end of the T-box; a carrier plate slidably secured to an upper side the anchor plate and latched to the T-box; a saddle bracket secured to a lower side of the anchor plate and latched to the T-box, and a pair of clamp blocks on opposite sides of the anchor plate fixed to sparger pipes coupled to the T-box.

Abstract: A fuel assembly for a pressurized water reactor that has a protective grid attached to the bottom nozzle through a spacer insert captured between a control rod guide thimble end plug and the bottom nozzle. A thimble screw attaches the bottom nozzle to the control rod guide thimble end plug through a central opening in the spacer insert. The control rod guide thimble end plug is provided with a raised annular boss that encircles the thimble screw shank and rests against the upper surface of the bottom nozzle through the opening in the spacer insert. The opening in the spacer insert is large enough to provide both an axial and radial clearance between the spacer insert and the end plug to accommodate differences in thermal expansion.

Abstract: [Problem] To facilitate mounting of a nozzle. [Solving Means] In a nozzle mounting structure for mounting a nozzle 20 penetrating through a reactor vessel 10 having a hemispherical concave inner surface, the nozzle mounting structure includes a removed concave portion 17 in which a base material 12 on an inner surface side of the reactor vessel 10 is removed in a symmetrical shape around a normal line N on the hemispherical concave inner surface of the reactor vessel 10, a flange 25 provided on the nozzle 20, formed in a same symmetrical shape as that of the removed concave portion 17 around the normal line N, and inserted into the removed concave portion 17, and a weld part 18 provided around the normal line N for welding the flange 25 to the reactor vessel 10.

Abstract: An emergency core cooling system directly injects emergency core cooling water, which is supplied from a high-pressure safety injection pump or a safety injection tank for a pressurized light water reactor, into a reactor vessel downcomer. A pipe connector is completely removed from between each direct vessel injection nozzle and each injection extension duct installed on an outer surface of the core barrel, which are opposite to each other. An emergency core cooling water intake port, through which the water is injected from each direct vessel injection nozzle, is formed on the surface of each injection extension duct facing an axis of each direct vessel injection nozzle. Thereby, a structure in which a jet of the emergency core cooling water flows into the injection extension ducts is adopted in a hydraulic connection fashion.

Abstract: Disclosed embodiments include nuclear fission reactor cores, nuclear fission reactors, methods of operating a nuclear fission reactor, and methods of managing excess reactivity in a nuclear fission reactor.

Abstract: A debris filter bottom nozzle for a pressurized water nuclear reactor fuel assembly that employs a corrugated screen in combination with flow through holes in an adapter plate to filter out potentially damaging debris. The area between the screen and the adapter plate defines a plenum that forms a collection point for the debris and coolant access is provided to the plenum through openings in the screen and sidewalls of the nozzle.

Abstract: A nuclear fuel assembly bottom nozzle, of the type including a perforated plate to allow water to pass through it, the nozzle having lateral faces, and at least one anti-debris element positioned on a lateral face to block out debris likely to infiltrate between the bottom nozzle and another adjacent bottom nozzle, characterized in that, in the free state, the or each anti-debris element permanently projects from the lateral face on which it is positioned, the or each anti-debris element being elastically deformable so as to retract towards the lateral face in the event of a force being exerted on the anti-debris element towards the lateral face.

Abstract: The invention relates to a pressurised water nuclear reactor vessel, comprising: an outer casing which comprises at least one cylindrical shell and a dished bottom head, a core support plate, a vessel bottom head space being delimited between the support plate and the dished bottom head, the support plate being perforated with holes for circulation of the primary coolant which place the vessel bottom head space in communication with the core, a calming device which is arranged in the vessel bottom head space, wherein the calming device comprises at least one calming plate which is substantially perpendicular relative to the centre axis of the vessel and a plurality of calming holes, the calming holes being provided in the calming plate and being capable of calming the primary coolant by passing the fluid through the holes.

Abstract: A debris filter bottom nozzle for a nuclear fuel assembly having a support skirt and a top plate. The top nozzle plate has defined therethrough a plurality of flow holes. The axial bore through each flow hole is contoured as a venture. Preferably, the venturi is formed with a double chamfered inlet.

Abstract: A direct vessel injection (DVI) nozzle for minimum emergency core coolant (ECC) bypass is disclosed. The DVI nozzle is used in a pressurized light water reactor (PLWR) having a reactor vessel with a reactor coolant system in which a coolant flows into the reactor vessel through a cold leg and passes through a reactor core prior to being discharged to the outside of the reactor vessel through a hot leg. The DVI nozzle, provided to directly inject ECC into the reactor vessel to cool the reactor core during a break in the reactor coolant system, such as a cold leg break (CLB) that may occur in the PLWR, is placed on the reactor vessel at a position horizontally offset from the central axis of the hot leg at an angle of 10° to 30° and is involved within a region defined above the central axis of the hot leg by a distance of 1.5 times the sum of diameters of the hot leg and the DVI nozzle.

Abstract: A core spray sparger T-box attachment assembly for a nuclear reactor pressure vessel, wherein the pressure vessel includes a shroud, a sparger T-box penetrating the shroud, a plurality of sparger distribution header pipes coupled to the sparger T-box, and a downcomer pipe. The sparger header pipes may include at least one sparger nozzle, and the sparger T-box attachment assembly may include a downcomer pipe coupling and a sparger T-box clamp. The sparger T-box clamp may include an anchor plate having a draw bolt opening to receive a draw bolt, a first clamp block substantially aligned at one end of the anchor plate, and a second clamp block substantially aligned at the other end of the anchor plate.

Abstract: This bottom end-piece includes nozzles for directing the flow of water of the reactor along the lower ends of the fuel rods, the nozzles being arranged at nodes of the substantially regular network of the fuel rods, and an anti-debris device which delimits water flow channels. At least some of the water flow channels are arranged at nodes of the substantially regular network. Direction nozzles are arranged at least partially in the channels in order to delimit water passages therewith, and at least one water passage includes a first section and a second section which are mutually offset radially relative to the corresponding node of the network in order to form a baffle.

Abstract: A core spray T-box attachment assembly for a core spray nozzle includes a primary cruciform wedge and a secondary cruciform wedge in contact with the primary cruciform wedge to form a cruciform wedge subassembly adapted for insertion within a bore of the core spray nozzle to sealingly engage an interior converging portion of a safe end of the core spray nozzle. The assembly includes a spider in contact with the cruciform wedge subassembly, and a draw bolt engaging an axial bore of a center portion of the cruciform wedge subassembly and the spider to the T-box.

Abstract: Provided is a fuel assembly 1 for a PWR nuclear reactor capable of stably creating transverse flows of coolant for pressing and securing control rods so as to restrain vibration of the control rods in order to restrain the outer surfaces of the control rods and the inner surfaces of control rod guide tubes from being worn, wherein an upper nozzle arranged above the fuel assembly comprises an adapter plate 6 constituting the lower structure of the upper nozzle, a side wall extended along the periphery of the adapter plate, an overhang projected into a space above the adapter plate from the upper part of the side wall, and apertures for attaching control guide tubes and passage holes, which are formed in the passage surface of the adapter plate, and wherein those 15A, 15B, 15C of the passage holes which are located at positions where the coolant impinges upon the overhang are generally arranged, line-symmetric with respect to diagonal lines of the passage surface serving as symmetric axes Q, and ligaments 21, 2

Abstract: A drainage apparatus and a drainage method for a reactor coolant system are disclosed. According to the drainage apparatus and the drainage method, the gravity drainage procedure for performing the decomposition maintenance of a main valve forming the pressure boundary part between the RCS and the safety injection system is improved by a forced drainage procedure using a drainage pump, and there are the effects that working period for a planned preventive maintenance is shortened, liquid waste of a coolant of the reactor is not generated, reprocessing costs are decreased, and the economical efficiency and the safety of the nuclear power plant are improved.

Abstract: A fuel inlet mechanism to introduce a coolant into a fuel assembly configured to be charged in a light water nuclear reactor, includes, a filter catching a foreign substance included in the coolant on an upstream side of the fuel assembly, the filter having a plurality of through holes to pass the coolant, and the through holes having an inlet portion, an outlet portion and at least one bent portion to a degree by which the outlet portion cannot be seen through from the inlet portion by a straight line.

Abstract: A reactor tube apparatus for a gas and liquid reactor, particularly for use in a Fischer-Tropsch process is disclosed. The apparatus comprises modified reactor tubes for use with a gas cap. Preferred embodiments of the reactor tubes have a slit or aperture which allows a limited amount of liquid to enter the reactor tube before the liquid level reaches the rim of the reactor tube. Thus liquid enters the reactor tubes more gradually which reduces surges of liquid and provides a more consistent dissipation of heat within the reactor tubes.

Abstract: A core disposed in a reactor pressure vessel includes one layer (an outermost region) at an outermost side of the core, two-three layers (an outer region) inside the outermost region and other layers (an inner region) inside the outer region. Fuel assemblies arranged in the core are supported by fuel supports having orifice. Orifice pressure loss coefficient of the orifice in the outermost region is set to be maximum and the orifice pressure loss coefficient of the orifice in the outer region is set to be minimum such that the flow rate of the coolant W for each fuel assembly in the outermost region is lowest and that for each fuel assembly in the outer region is highest. In the core of the natural circulation boiling water reactor, the reactor power distribution in a radial direction is flattened, and it is possible to increase the thermal margin.

Abstract: In a nuclear reactor internal structure, generation and promotion of object-downstream separating vortices are suppressed so that coolant uniformly flows in a reactor core and pressure loss of flow of the coolant is reduced so that the flow of the coolant is stabilized. A lower connecting plate 30 arranged in a lower plenum 8 comprises a ring portion 31 in which an arcuate portion 32 and a cut-off portion are alternately formed. An outer peripheral portion of the ring portion 31 is asymmetric relative to a flow direction of main flow and also asymmetric relative to a separating flow generation direction.

Abstract: In the method, a set of limits applicable to a core may be defined, and a test core loading pattern design, to be used for loading the core, may be determined based on the limits. Reactor operation on at least a subset of the core may be simulated to produce a plurality of simulated results. The simulated results may be compared against the limits, and data from the comparison may indicate whether any of the limits were violated by the core during the simulation. A designer or engineer may use the data to modify the test core loading pattern, creating one or more derivative core loading pattern design(s) for simulation and eventual perfection as an acceptable core loading pattern design for the core.

Abstract: A resistance member (e.g., fuel holding portion of the lower tie plate) is provided at the lower end of the fuel assembly. Provision is made of a coolant ascending path in which said water rods have coolant inlet ports that are open in a region lower than the resistance member to upwardly guide the coolant, and a coolant descending path which has a coolant delivery port that is open in a region higher than the resistance member to downwardly guide the coolant. The coolant ascending path and the coolant descending path are communicated with each other at their upper end portions.